Ink jet printing is a non-impact method for producing printed images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital data signals. There are various methods that may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired printed image. In one process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired printed image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. In another process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an image-wise manner onto the surface of the image-recording element, while un-imaged droplets are caught and returned to an ink sump. Ink jet printers have found broad applications across markets ranging from desktop document and photographic-quality imaging, to short run printing and industrial labeling.
The ink compositions known in the art of inkjet printing may be aqueous- or solvent-based, and in a liquid, solid or gel state at room temperature and pressure. Aqueous-based ink compositions are preferred because they are more environmentally friendly as compared to solvent-based inks, and most printheads are designed for use with aqueous-based inks.
The ink composition may be colored with pigments, dyes, polymeric dyes, loaded-dye/latex particles, or any other types of colorants, or combinations thereof. Pigment-based ink compositions are advantageous because such inks render printed images giving comparable optical densities with better resistance to light and ozone image degradation as compared to printed images made from other types of colorants. The colorant in the ink composition may be yellow, magenta, cyan, black, gray, red, violet, blue, green, orange, brown, etc. These inks may further contain polymeric binders.
Although numerous ink compositions are known in the art of inkjet printing, several key challenges remain. One challenge is to obtain the highest possible image quality on a variety of inkjet receivers. It is further desirable to obtain the highest optical density for a given amount of ink applied to an inkjet receiver, especially on plain papers.
A further challenge for inks comprising both pigments and polymeric binders is managing their ability to function in the printer system. Ink must properly wet felt employed to regulate pressure in a printhead so that flow of ink through the printhead occurs only when desired. Management of the surface tension of inks is also required to enable delivery of ink through a printhead in addition to aiding wetting of the surface of the substrate to which the ink is applied.
In addition to the desirability for an ink to have a good optical density when printed on plain paper, there are a number of constraints on the physical properties of an inkjet ink so that it can function effectively in an inkjet printer and make a lasting image. These properties include viscosity and rheology, ink physical stability, redispersibility of dried ink for circulating systems, surface tension and wetting, and jetting performance including drop formation stability, satellite suppression, print window, latency, and repeated firability. It is also important that inks dry fast on the paper, do not repel one another, and absorb into the substrate without bleeding when over printed with different colors. The dried inks need to have good image permanence including fade and scratch resistance.
To provide desired performance, inkjet printing fluid compositions may include various water soluble or dispersible polymers, dispersing aids to prevent flocculation of dispersed materials, and surfactants.
U.S. Pat. No. 4,680,332 describes a heterophase ink with a water insoluble polymer, a solvent soluble dye and a nonionic stabilizer permanently attached to the polymer, dispersed in water and alcohol; ST 45 to 65 dynes/cm. The stabilizer is either: an EO-PPO block copolymer such as Pluronic F68, poly(ethylene oxide) tertiary octylphenol, poly(vinyl alcohol), poly(acrylic acid), hydroxypropyl cellulose, poly(vinyl pyrrolidone), poly(ethylene oxide), poly(ethylene imine), or poly(ethylene oxide)monomethyl ether. This patent discloses the use of a blend of polymers for improved ink performance, specifically an insoluble polymer with a PEO containing nonionic stabilizer polymer. The polymer blend principally allows incorporation of oil soluble dyes in an aqueous ink formulation.
U.S. Pat. No. 5,180,624 discloses an ink receiving layer with polymer binder, silica, cationic polymers etc which is coated on top of paper. This patent discloses using one or more water soluble polymer fillers with good ink affinity and includes a long list of polymers which includes both PEO and PAM polymers, alone or in combination, to form an ink receiving layer.
U.S. Pat. No. 7,004,579 discloses a large variety of polyvinyl ether block copolymers which are complexed with various functional groups to impart temperature, pH, and evaporation sensitivity and yield inks that respond to these stimuli. The PEO containing diblock copolymers described are directly covalent bound to black or colored pigments.
U.S. Pat. No. 7,556,680 discloses a pigmented ink with an added amide compound such as uracil, thymine, sarcosine anhydride, glycine, and alanine, to improve the stability of the ink, water fastness, and wet and dry rub performance. This patent discloses oligomeric amide compounds used with low Mw PEOs (400-600) in carbon black inks.
U.S. Pat. No. 6,475,271 discloses a black ink with PAM and PEO polymer added together for the purpose of obtaining low intercolor bleed and improved MFLEN (mid frequency line edge noise) for carbon blacks by adding two low boiling alcohols or thiols (<115C and <135C BP). Example 6 of this patent discloses PEO at 0.05 weight percent and PAM at 0.5 weight percent together in a black ink.
U.S. Pat. No. 7,878,643 discloses dye-based ink formulations with preferable ranges for dynamic surface tension at 50 ms and at 500 ms lifetimes, as determined by maximum bubble pressure method (referred to herein as MBP nominal surface age, or MBP age), with a difference between these dynamic surface tensions of 7 mN/m or more.
U.S. Pat. No. 7,862,653 teaches that it is desirable to have the dynamic surface tension of the ink to be at least 49 mN/m or more at a lifetime of 50 milliseconds as determined by MBP method for improved optical density. The patent further discloses that this ink preferably have a difference between the dynamic surface tension at a lifetime of 50 milliseconds (MBP method) and the dynamic surface tension at a lifetime of 5,000 milliseconds (MBP method) of 15 mN/m or more to obtain improvements in both optical density and fixing ability.
Controlling surface tension using fluorinated surfactants has been employed in various ink formulations in the art, frequently in combination with the use of other classes of surfactants where either or both surfactants are at relatively high concentrations in the inks, such as in U.S. Patent Application 2007/0120928. In some cases, the fluorinated surfactants are disclosed in formulations without other surfactants, such as in the following publications: U.S. Patent Application 2008/0049086, U.S. Patent Application 2006/0116439, U.S. Pat. No. 7,478,902, U.S. Pat. No. 7,622,513, and U.S. Pat. No. 7,696,262.
It would be desirable to develop new inkjet printing fluid compositions with unique combinations of materials selected to further improve inkjet printing performance.